Use Groovy dynamic language to write scripts using ImageJ API. Have full access to ImageJ API and API's of all installed plugins. Tutorials and code examples are available.
Plugins > Scripting > Groovy Console - Opens Groovy Console with access to ImageJ class loader enabling access to ImageJ and all installed plugins.
Plugins are distributed in file ij-groovy_.jar available in ij-groovy package at: http://ij-plugins.sourceforge.net/.